When an air conditioner operates under heating mode with relatively high outdoor temperatures, the indoor heat exchanger (i.e., the indoor unit) often overheats. Otherwise when the air conditioner operates in cooling mode with relatively low outdoor temperatures, the indoor heat exchanger (i.e., the indoor unit) temperature would usually run too low. To prevent such situations from happening, the compressor is typically stopped for protection.
After being started, the compressor usually needs to operate at a preset frequency such as around 60 or 90 Hz for over 1 minute. However, if the compressor operates at such frequencies whether under the heating mode with relatively high outdoor temperatures or under the cooling mode with relatively low outdoor temperatures, the evaporator temperature would very soon reach the high or low temperature protective value. Thus, the system implements protection once about every 5 to 7 minutes, resulting in frequent restarts of the compressor.